Compound archery bows typically are of the so-called dual-cam design, originated in U.S. Pat. No. 3,486,495. Bows of this type typically comprise a bow handle having limbs mounted on and extending from opposed ends of the handle. Power let-off cams are rotatably mounted on the free ends of the bow limbs and are interconnected by one or more cable sections including a draw string section. As the bow draw string is drawn away from the handle, draw force initially increases as the limbs are drawn together and the cams rotate to a power let-off point, and thereafter the leverage increases and the draw force decreases as the cams rotate further but with little additional limb flexure. This so-called compound action allows full bow draw to be maintained at lesser force without fatigue to the archer. A problem inherent in dual-cam bows of this type lies in the fact that the cams must be closely matched and synchronized with each other in order to insure straight-line (or substantially straight-line) travel of the nock point on the bow string, and the limbs must be closely balanced and evenly stressed as the string is drawn. Damage to or mismatching of the cams, mismatch or incorrect adjustment of the limbs, or stretching of the cable sections can cause loss of synchronization between the cams and uneven stressing of the limbs, resulting in less than optimum performance of the bow.
In order to overcome the aforementioned deficiencies of dual-cam bows, it has heretofore been proposed to provide a compound bow that has a single power let-off cam disposed at the end of one bow limb, and a control pulley or wheel disposed at the end of the opposing limb over which the bow string is trained. U.S. Pat. No. 5,505,185 discloses such a single-cam compound bow. A control cable cooperates with the power let-off cam and a control groove in the control wheel to maintain the desired relationship or timing between bow string take-up grooves in the control wheel and power cam. In this way, identical or substantially identical incremental bow string cable travel to and from the bow string take-up grooves is obtained, thereby yielding straight-line nock travel as the bow string cable is drawn and released. A power cable extends from the power cam to the opposing bow limb for flexing the bow limbs uniformly as the bow string is drawn, and for cooperating with the power cam to obtain the power let-off action that is characteristic of compound bows.
Although the single-cam compound bow disclosed in the noted copending application addresses and overcomes many problems theretofore extant in the art, further improvements remain desirable. In particular, the noted application does not disclose any means or technique for adjusting draw length of the bow. That is, the bow disclosed in the noted application obtains straight-line nock travel for a given bow draw length for which the power cam and the control wheel are designed. In order to change or adjust bow string draw length, the power cam and/or the control wheel must be changed to accommodate the new desired draw length while maintaining synchronous timing between the cam and wheel. In a commercial single-cam compound bow of a different design, accommodation is made for changing the bow string cable anchor point at the power let-off cam, and thereby changing the bow string draw length. However, since the cams and wheels are optimized for only a single draw length, changing the bow string anchor point inherently changes the path of nock travel as the bow is drawn and released, and consequently affects accuracy of the bow.
Another problem in single-cam compound bows heretofore proposed lies in the creation of a torque or twisting force on the bow limb that carries the power let-off cam, which varies as the bowstring is drawn and released. Bow limb torque is not a problem at the limb that carries the control wheel because the power cable segment can be anchored to the limb at both sides of the control wheel, and because the cable groove or grooves in the control wheel can be placed very close to the limb centerline. However, at the power cam, the bow string, power cable and control cable segments engage the cam at laterally spaced positions. These cable segments apply a torque through the cam axle to the bow limb. This problem is exacerbated when a cable guard is employed on the bow because the cable guard offsets the control and power cable segments from the bow limb centerline.
It is therefore a general object of the present invention to provide a compound bow that obtains the benefits of single-cam compound bow designs as compared with dual-cam designs--i.e., obtains uniform stressing of the bow limbs and straight-line (or substantially straight-line) nock travel--for a range of draw lengths. That is, an object of the present invention is to provide a single-cam compound bow in which the bow string draw length can be adjusted without deleteriously affecting other salutary operating characteristics of the bow. A more specific object of the present invention is to provide a single-cam compound bow of the described character in which bow string draw length can be adjusted by adjusting and/or replacing draw length modules on the bow power cam. A further and related object of the present invention is to provide a single-cam compound bow of the described character that obtains the foregoing objectives while employing standard cable lengths for economy of manufacture and service. Yet another object of the present invention is to provide a single-cam compound bow that has a positive bow string draw stop, which is deemed particularly desirable by archery enthusiasts, that automatically adjusts with draw length. A further object of the invention is to provide a single-cam compound bow in which torque applied to the power-cam limb, as the bow is drawn and released, is reduced or eliminated.